This invention relates to an ice-cream maker including a freezing tank provided with a heating system for pasteurizing its contents. The invention, more particularly, relates to such an ice-cream maker provided with a storage container for ice-cream mix which is connected, by at least one supply line, to the freezing tank.
One such ice-cream maker, known from U.S. Pat. No. 3,930,535, has a freezing tank in the form of a cylindrical housing which is surrounded by a heating jacket equipped with heating elements, as well as a cooling jacket equipped with cooling ducts. The heating system is dimensioned and controlled, in such a manner that the inside wall of the freezing tank is brought to a temperature which causes the ice cream mix in the freezing tank to partially evaporate. This vapour rises via a refill pipe into a storage container arranged above the freezing tank and heats the contents of the former to a temperature of from 70.degree. to 80.degree. C. (corresponding from 343.degree. to 353.degree. K.), which is sufficient for pasteurization. An appropriate thermostatic control ensures that the inside walls of the freezing tank do not assume a temperature which lies much above 100.degree. C. (373.degree. K.), in order to prevent the ice-cream mix from sticking to the inside wall of the freezing tank.
This known ice-cream maker has been extraordinarily successful in practice and, in particular, has achieved extremely good bacteriological results, that is, the ice cream has always been bacteriologically satisfactory. However, heating the contents of the storage container, arranged above the freezing tank, by means of steam generated in the freezing tank, leads to the heating-up process, that is, the pasteurization process, for pasteurizing the contents of the storage chamber, having to take a very long time, for example, one-and-a-half hours. This relatively long time has been extended still further by the fact that, as mentioned, the temperature of the heat-transmitting inner wall of the freezing tank was not allowed to exceed certain temperatures, lying not very far above the vaporization point of water, in order to prevent the ice-cream mix from sticking. Since, in addition, as a result of this slow heating up, the ice-cream mix also remains for a relatively long period in temperature ranges of from between 35.degree. and 45.degree. C. (corresponding to from 308.degree. to 318.degree. K.), in which germs will multiply particularly rapidly, the ice-cream mix had to be maintained for an especially long time at the temperature of pasteurization.
This long thermal treatment of the ice-cream mix at temperatures between from 70.degree. and 80.degree. C. in the storage container, and at temperatures of around 100.degree. C., or just under in the freezing tank, however, led to changes in the flavour of the ice-cream mix (which, of course, is normally produced with a milk base). This long thermal treatment leads to a certain caramelization of the ice-cream mix, that is, to undesirable changes in flavor.
From German Offenlegungsschrift (Laid Open Patent application) No. 20 32 003 and, similarly, from German Offenlegungschrift (Laid Open Patent application) No. 26 57 534, in each case an ice-cream maker is known in which underneath the freezing tank a separate, that is, transportable, storage container is arranged in a releasable and interchangeable manner in a cooling chamber and is connected via a flexible connecting line to a freezing tank, on the one hand, and with another flexible connecting line to a source of compressed air. The designs of these known ice-cream makers are not concerned with bacteriological problems. Constructing the storage containers as separate, releaseable and interchangeable storage containers is merely meant to make it possible to construct them as hermetically closed units so that the ice-cream mix is not contaminated bacteriologically during transport. None of the bacteriological problems occurring actually in the ice-cream maker and particularly during its operation are dealt with.
From U.S. Pat. No. 3,811,494, it is known to connect, with ice-cream makers comprising a freezing tank which is spatially separated from the storage container, both of these to one another by a forward-flow line and a return-flow line so that constant pumping is possible. The purpose of this is to prevent, on the one hand, the ice-cream mix present in the lines from warming up during a prolonged stand-still due to mix removal, and germs from multiplying as a result of this. On the other hand, this measure serves to make it possible to pasteurize also the contents of the lines during the pasteurization process and, in addition, to manage, if necessary, with only one heating system for pasteurizing the contents of the freezing tank and of the storage container and the two lines.